[TySan] false positive with unions and placement-new

[Jannik2099]

According to https://eel.is/c++draft/class.union#general-6 , the active union member in an union of non-POD types can be switched by invoking the dtor of the old member, and placement new-ing into the new member.

However, tysan does not seem to like this https://godbolt.org/z/nvnjzjGez

#include <cstdio>
#include <new>

class Foo {
   private:
    short i{};

   public:
    Foo() { printf("Foo nontrivial ctor\n"); }
    ~Foo() { printf("Foo nontrivial dtor\n"); }
};

class Bar {
   private:
    int i{};

   public:
    Bar() { printf("Bar nontrivial ctor\n"); }
    ~Bar() { printf("Bar nontrivial dtor\n"); }
};

union U {
    Foo foo;
    Bar bar;
    ~U() {}
};

int main() { 
    U u{ .foo = {}};
    u.foo.~Foo();
    new (&u.bar) Bar;
}

==1==ERROR: TypeSanitizer: type-aliasing-violation on address 0x7ffff9117e2c (pc 0x61eed1b9b89d bp 0x7ffff9117d10 sp 0x7ffff9117cb8 tid 1)
WRITE of size 4 at 0x7ffff9117e2c with type int (in Bar at offset 0) accesses an existing object of type short (in Foo at offset 0)
    #0 0x61eed1b9b89c  (/app/output.s+0x2b89c)

This also happens with an union of POD or trivial types, but I'm not 100% sure on the standard wording if placement-new is supposed to be allowed in these cases.